A water cleaning device is known which comprises a housing arranged to be supported on a surface, the housing defining a receptacle for water to be cleaned and a water filtration unit removably mounted to a mounting support provided by the housing and an electrically operated pump and control means for controlling the pump provided within the housing for pumping water through the filtration unit to provide cleaned filtered water at an outlet of the water filtration unit.
U.S. Pat. No. 3,950,253 describes such a water cleaning device in which the filtration unit is mounted within the water receptacle mainly by means of a fluid-tight seal between a nipple connected to the pump outlet and mounted in the base of the receptacle and an inlet bore of the filtration unit. An O-ring seal is provided between the nipple and the inlet bore to ensure a water-tight seal. The filtration unit is inserted into the housing through an opening at the upper part of the housing. The opening may define a frame giving positional support to the filtration unit. The filtration unit may be provided with wing members intended to align with corresponding edges of the frame to enable the filtration unit to be correctly located within the receptacle.
Although the device described in U.S. Pat. No. 3,950,253 may enable a filtration unit to be correctly located, the device cannot identify whether or not a filtration unit which has just been inserted is a new unused filtration unit and accordingly it is possible for a user of the device accidentally to insert an old used filtration unit into the device.
As the user would be unaware that an old used filtration unit which has become clogged or is otherwise no longer fully operational had been inserted into the device, the user may then proceed to operate the device with the used filtration unit and the device would then no longer provide good quality filtered water.